Some electrical devices such as communication devices that are sold commercially require approval by one or more testing agencies or governmental regulatory bodies. Such testing agencies include Underwriter's Laboratories (UL), Factory Mutual (FM) and the British Approval Board for Telecommunications (BABT). For example, in the United Kingdom, the BABT requires that communication devices which are to be connected to the telephone lines be provided with enough electrical isolation between the user and the electronic equipment in order to prevent electrical shock to the device user. In the case of a second generation cordless telephone (CT-2) base unit, British Standard 6301 (dated 1989) requires restricted access for any exposed conductive parts by the device user.
Expensive isolation transformers and relays must be typically used to isolate the AC and telephone line connections which are coupled to the unit, in order to meet the standards imposed by the testing agencies. The agencies are concerned specifically with users receiving dangerous electrical shock from exposed conductive lines and also with preventing dangerous voltages from coupling to the telephone lines. In the specific case of a unit having back-up batteries, isolation to the exposed battery contacts once the battery compartment cover is removed must also be provided, adding more cost to the communication device (e.g, cost of adding more isolation transformers, etc.). A need thus exists for a way of meeting some of these testing agency standards for electrical isolation and at the same time reducing the need for isolation transformers and relays which add cost to a communication device.